Assuming no or minimal congestion or losses, the LMP (locational marginal price) or nodal price is basically the same everywhere. So the question is what is the MEC (marginal energy component) of the nodal price which is shared by everyone. In general, prices in the spot market are pretty low that early in the morning. It depends on the RTO/ISO region, but maybe ~$10/MWh?
Using lithium ion batteries, that solar would cost $81-$140/MWh, which is pretty much the same price as coal (compare the final slide to the first slide):
But batteries get cheaper every year, so check back in 2021 for even cheaper prices. Most observers expect lithium ion storage to be cheaper than natural gas within a decade. And when you amortize the nighttime storage costs with the cheap daytime solar, natural gas is barely holding on in some markets. If we had a carbon tax that came close to internalizing the externalities, I don't think NG would be running for much longer.
With 4500km power transmission lines currently being planned[1], the key question is "1 am where?" That's about 3-4 hours of time difference if the cable was along a line of latitude which obviously reduces the required storage time.
